This invention relates to a method of winding rapidly running thread, for example composed of glass fibres, on to a bobbin. The invention further comprises an apparatus for carrying out the method of the invention.
In the performance of winding a bobbin it is customary to apply a cross-winding using a thread guide which is subject to a plurality of different components of movement in the axial direction of the bobbin. The formation of a cross winding on bobbin produces an orderly compact structure of a roughly cylindrical external shape. Generally a thread guide controlled by a cross-grooved shaft is used to implement the cross winding. The cross-grooved shaft has two screw threads of comparatively steep pitch, one being a right-hand and the other a left-hand thread. A guide block or tenon carried or controlled by the thread guide engages in the screw threads, and devices are provided at the ends of the cross-grooved shaft to conduct the guide block or tenon from one screw thread to the other so that, with a uniform rotation of the cross-grooved shaft, the guide block carries out reciprocating movements at a substantially uniform speed. It will be apparent that delays and accelerations are produced at the time of reversal of the operation.
Satisfactory results are obtained with cross-grooved shafts at moderate winding speeds. Where, however, extremely high winding speeds are required, as for example is the case of glass fibre manufacture, a cross-grooved shaft is not entirely satisfactory. The forces generated by the great acceleration and retardation at the reversing ends of the shaft produce considerable wear during the transfer of the guide block from one thread to the other.
These acceleration and retardation forces can be reduced if the thread guide is devised to carry out a more harmonic movement. This however is not feasible because a substantially cylindrical wound package shape can only be achieved if the thread guide has consistently imposed thereon the same period of operation at every point of the bobbin circumference.
It is known to guide the thread by means of a slotted jacket through which it is delivered to the bobbin. This arrangement does not however allow for the production of a cylindrical bobbin at the high speeds referred to, and indeed the result of using this arrangement is that the winding assumes a frustoconical shape at its ends, as a consequence of which the quantity of thread in a package is considerably reduced.
It is already known to impose different components of movement to the thread guide, using a slotted jacket as the guide but, in this case the axial zone along which the slotted jacket can move is comparatively small. To enable the whole length of the bobbin to be reached the jacket itself is provided with its own drive, and is reciprocated along the complete bobbin. This art of laying in the thread, in which the cross-grooved shaft operates at substantially lesser speeds and the aforementioned difficulties are thereby avoided, does not in fact produce a useful result. There is a substantial flattening out in the zone of the ends with the increased danger that the end windings will not remain secure and will tend to loosen and drop off when winding off occurs, thus delaying the operation of the units served.
A further difficulty in the known winding methods referred to above resides in the fact that the end of the thread is not conspicuous in the finished package. This often results from the irregular appearance of the package with the end of the thread hidden. Finding the end of the winding involves further trouble and expense.
Again, a bobbin which is not sufficiently of cylindrical shape, but is of frustoconical form at the ends, produces difficulties during the run-off of the thread. If the thread is wound from the smaller diameters, the pull is less than that in the area of the larger diameter.